Copolymer, rubber composition using same, and tire

ABSTRACT

The present invention relates to a copolymer including a monomer unit (a) derived from isoprene and a monomer unit (b) derived from farnesene; a process for producing the copolymer including at least the step of copolymerizing isoprene with farnesene; a rubber composition including (A) the copolymer, (B) a rubber component and (C) carbon black; a rubber composition including (A) the copolymer, (B) a rubber component and (D) silica; a rubber composition including (A) the copolymer, (B) a rubber component, (C) carbon black and (D) silica; and a tire using the rubber composition at least as a part thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Non-Provisional applicationSer. No. 14/390,660 (issued as U.S. Pat. No. 9,732,206), which was filedon Oct. 3, 2014. Application Ser. No. 14/390,660 was the National Stageof PCT/JP2013/060128, which was filed on Apr. 2, 2013. This applicationis based upon and claims the benefit of priority to Japanese ApplicationNo. 2012-085929, which was filed on Apr. 4, 2012.

TECHNICAL FIELD

The present invention relates to a copolymer containing a monomer unitderived from farnesene, a rubber composition containing the copolymer,and a tire using the rubber composition.

BACKGROUND ART

Hitherto, in the application field of tires for which a wear resistanceand a mechanical strength are required, there have been extensively usedrubber compositions that are enhanced in mechanical strength byincorporating a reinforcing agent such as carbon black in a rubbercomponent such as a natural rubber and a styrene-butadiene rubber. It isknown that the carbon black exhibits its reinforcing effect byphysically or chemically adsorbing the aforementioned rubber componentonto a surface of respective particles of the carbon black. Therefore,when the particle size of the carbon black used in the rubbercomposition is as large as from about 100 to about 200 nm, it isgenerally difficult to attain a sufficient interaction between thecarbon black and the rubber component, so that the resulting rubbercomposition tends to be hardly improved in mechanical strength to asufficient extent. In addition, tires produced from such a rubbercomposition tend to exhibit a low hardness and therefore tend to beinsufficient in steering stability.

On the other hand, when the carbon black used in the rubber compositionhas an average particle size as small as from about 5 to about 100 nmand therefore a large specific surface area, the resulting rubbercomposition can be improved in properties such as mechanical strengthand wear resistance owing to a large interaction between the carbonblack and the rubber component. In addition, tires produced from such arubber composition can be improved in steering stability owing to anincreased hardness thereof.

However, in the case where the carbon black having such a small averageparticle size is used in the rubber composition, it is known that theresulting rubber composition tends to be deteriorated in dispersibilityof the carbon black therein owing to a high cohesive force between thecarbon black particles. The deteriorated dispersibility of the carbonblack in the rubber composition tends to induce a prolonged kneadingstep and therefore tends to give an adverse influence on productivity ofthe rubber composition. Also, the deteriorated dispersibility of thecarbon black tends to cause generation of heat in the rubbercomposition, so that tires produced therefrom tend to be deteriorated inrolling resistance performance and may frequently fail to satisfy therequirements for low rolling resistance tires, i.e., so-called low-fuelconsumption tires. Furthermore, in the case where the carbon black usedin the rubber composition has a small average particle size, there tendsto occur such a problem that the resulting rubber composition exhibits ahigh viscosity and therefore is deteriorated in processability.

Thus, the mechanical strength and hardness of the rubber composition fortires are properties having a contradictory relation with the rollingresistance performance and processability thereof, and it is thereforeconsidered that the rubber composition is hardly improved in both of theproperties in a well-balanced manner.

In Patent Document 1, as a rubber composition that can be improved inthe aforementioned properties in a well-balanced manner, there isdescribed the rubber composition for tires which includes a rubbercomponent containing an isoprene-based rubber and a styrene-butadienerubber, carbon black and a liquid resin having a softening point of from−20 to 20° C. at a specific compounding ratio.

Also, Patent Document 2 describes the tire including a rubber componentcontaining a diene-based rubber constituted of a modifiedstyrene-butadiene copolymer and a modified conjugated diene-basedpolymer, and a filler such as carbon black at a specific compoundingratio.

However, any of the tires described in these Patent Documents fail tosatisfy the mechanical strength and hardness as well as the rollingresistance performance and processability with a sufficiently highlevel, and therefore there is still a strong demand for tires that arefurther improved in these properties.

Meanwhile, Patent Document 3 and Patent Document 4 describe a polymer ofβ-farnesene, but fail to have a sufficient study on practicalapplications thereof.

CITATION LIST Patent Literature

Patent Document 1: JP 2011-195804A

Patent Document 2: JP 2010-209256A

Patent Document 3: WO 2010/027463A

Patent Document 4: WO 2010/027464A

SUMMARY OF INVENTION Technical Problem

The present invention has been made in view of the above conventionalproblems. The present invention provides a copolymer capable ofenhancing a dispersibility of a filler such as carbon black and silicain a rubber composition when using the copolymer as a part of the rubbercomposition; a rubber composition that contains the copolymer, not onlyexhibits a good processability upon compounding, molding or curing butalso is excellent in rolling resistance performance and wear resistance,and further hardly suffers from deterioration in mechanical strength andhardness; and a tire obtained using the rubber composition.

Solution to Problem

As a result of extensive and intensive researches, the present inventorshave found that when using a copolymer containing a monomer unit derivedfrom isoprene and a monomer unit derived from farnesene in a rubbercomposition, the resulting rubber composition can be enhanced in notonly processability but also mechanical strength, wear resistance androlling resistance performance. The present invention has beenaccomplished on the basis of the above finding.

That is, the present invention relates to the following aspects.

-   [1] A copolymer including a monomer unit (a) derived from isoprene    and a monomer unit (b) derived from farnesene.-   [2] A process for producing the copolymer, including at least the    step of copolymerizing isoprene with farnesene.-   [3] A rubber composition including (A) the above copolymer; (B) a    rubber component; and (C) carbon black.-   [4] A rubber composition including (A) the above copolymer; (B) a    rubber component; and (D) silica.-   [5] A rubber composition including (A) the above copolymer; (B) a    rubber component; (C) carbon black; and (D) silica.-   [6] A tire using the above rubber composition at least as a part    thereof.

Advantageous Effects of Invention

According to the present invention, it is possible to provide acopolymer capable of enhancing a dispersibility of a filler such ascarbon black and silica in a rubber composition when using the copolymeras a part of the rubber composition; a rubber composition that containsthe copolymer, not only exhibits a good processability upon compounding,molding or curing but also is excellent in rolling resistanceperformance and wear resistance, and further hardly suffers fromdeterioration in mechanical strength and hardness; and a tire obtainedusing the rubber composition.

DESCRIPTION OF EMBODIMENTS

[Copolymer]

The copolymer according to the present invention is a copolymerincluding a monomer unit (a) derived from isoprene and a monomer unit(b) derived from farnesene.

In the present invention, the monomer unit (b) may be either a monomerunit derived from α-farnesene or a monomer unit derived from β-farnesenerepresented by the following formula (I). However, of these monomerunits, from the viewpoint of facilitated production of the copolymer,preferred is the monomer unit derived from β-farnesene. Meanwhile,α-farnesene and β-farnesene may be used in combination with each other.

The weight-average molecular weight (Mw) of the copolymer is preferablyfrom 2,000 to 500,000, more preferably from 8,000 to 500,000, still morepreferably from 15,000 to 450,000 and even still more preferably from15,000 to 300,000. When the weight-average molecular weight of thecopolymer falls within the above-specified range, the below-mentionedrubber composition has a good processability, and further can beimproved in dispersibility of the carbon black or silica compoundedtherein and therefore can exhibit a good rolling resistance performance.Meanwhile, the weight-average molecular weight of the copolymer as usedin the present specification is the value measured by the methoddescribed below in Examples. In the present invention, two or more kindsof copolymers that are different in weight-average molecular weight fromeach other may be used in the form of a mixture thereof.

The melt viscosity of the copolymer as measured at 38° C. is preferablyfrom 0.1 to 3,000 Pa·s, more preferably from 0.6 to 2,800 Pa·s, stillmore preferably from 1.5 to 2,600 Pa·s and even still more preferablyfrom 1.5 to 800 Pa·s. When the melt viscosity of the copolymer fallswithin the above-specified range, the resulting rubber composition canbe easily kneaded and can be improved in processability. Meanwhile, inthe present specification, the melt viscosity of the copolymer is thevalue measured by the method described below in Examples.

The mass ratio of the monomer unit (a) to a sum of the monomer unit (a)and the monomer unit (b) in the copolymer is preferably from 1 to 99% bymass, more preferably from 10 to 80% by mass and still more preferablyfrom 15 to 70% by mass from the viewpoint of enhancing a processabilityand a rolling resistance performance of the resulting rubbercomposition.

The molecular weight distribution (Mw/Mn) of the copolymer is preferablyfrom 1.0 to 4.0, more preferably from 1.0 to 3.0 and still morepreferably from 1.0 to 2.0. When the molecular weight distribution(Mw/Mn) of the copolymer falls within the above-specified range, theresulting copolymer can suitably exhibit a less variation in viscositythereof.

The copolymer according to the present invention may be any suitablecopolymer as long as it is produced at least by copolymerizing isoprenewith farnesene, and the copolymer may also be produced by copolymerizingthe other monomer with the isoprene and farnesene.

Examples of the other monomer include conjugated dienes such asbutadiene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene,1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 1,3-octadiene,1,3-cyclohexadiene, 2-methyl-1,3-octadiene, 1,3,7-octatriene, myrceneand chloroprene; and aromatic vinyl compounds such as styrene, α-methylstyrene, 2-methyl styrene, 3-methyl styrene, 4-methyl styrene,2,4-diisopropyl styrene, 2,4-dimethyl styrene, 4-tert-butyl styrene and5-tert-butyl-2-methyl styrene. Of these other monomers, preferred arebutadiene, myrcene, styrene, α-methyl styrene and 4-methyl styrene.

The content of the other monomer in the copolymer is preferably not morethan 50% by mass, more preferably not more than 40% by mass and stillmore preferably not more than 30% by mass.

[Process for Producing Copolymer]

The copolymer according to the present invention is preferably producedby the production process of the present invention which includes atleast the step of copolymerizing isoprene with farnesene. Morespecifically, the copolymer may be produced by an emulsionpolymerization method, a solution polymerization method or the like. Ofthese methods, preferred is the solution polymerization method.

(Emulsion Polymerization Method)

The emulsion polymerization method for producing the copolymer may beany suitable conventionally known method. For example, a predeterminedamount of a farnesene monomer and a predetermined amount of an isoprenemonomer are emulsified and dispersed in the presence of an emulsifyingreagent, and then the resulting emulsion is subjected to emulsionpolymerization using a radical polymerization initiator.

As the emulsifying reagent, there may be used, for example, a long-chainfatty acid salt having 10 or more carbon atoms or a rosinic acid salt.Specific examples of the emulsifying reagent include potassium salts andsodium salts of fatty acids such as capric acid, lauric acid, myristicacid, palmitic acid, oleic acid and stearic acid.

As the dispersant for the emulsion polymerization, there may be usuallyused water, and the dispersant may also contain a water-soluble organicsolvent such as methanol and ethanol unless the use of such an organicsolvent gives any adverse influence on stability of the polymerizationreaction system.

Examples of the radical polymerization initiator include persulfatessuch as ammonium persulfate and potassium persulfate; and organicperoxides and hydrogen peroxide.

In order to adjust a molecular weight of the resulting copolymer, theremay be used a chain transfer reagent. Examples of the chain transferreagent include mercaptans such as t-dodecyl mercaptan and n-dodecylmercaptan; and carbon tetrachloride, thioglycolic acid, diterpene,terpinolene, γ-terpinene and an α-methyl styrene dimer.

The temperature used upon the emulsion polymerization may beappropriately determined according to the kind of radical polymerizationinitiator used therein, and is usually preferably from 0 to 100° C. andmore preferably from 0 to 60° C. The polymerization method may be eithera continuous polymerization method or a batch polymerization method. Thepolymerization reaction may be stopped by adding a terminating reagentto the reaction system.

Examples of the terminating reagent include amine compounds such asisopropyl hydroxyl amine, diethyl hydroxyl amine and hydroxyl amine;quinone-based compounds such as hydroquinone and benzoquinone; andsodium nitrite.

After stopping the polymerization reaction, an antioxidant may be addedto the polymerization reaction system, if required. Furthermore, afterstopping the polymerization reaction, unreacted monomers may be removedfrom the resulting latex, if required. Thereafter, the resultingcopolymer is coagulated by adding a salt such as sodium chloride,calcium chloride and potassium chloride as a coagulant thereto and, ifrequired, while adjusting a pH value of the coagulation system by addingan acid such as nitric acid and sulfuric acid thereto, and then thedispersing solvent is separated from the reaction solution to recoverthe copolymer. The thus recovered copolymer is washed with water anddehydrated, and then dried to obtain the copolymer. Meanwhile, uponcoagulating the copolymer, the latex may be previously mixed, ifrequired, with an extender oil in the form of an emulsified dispersionto recover the copolymer in the form of an oil-extended rubber.

(Solution Polymerization Method)

The solution polymerization method for producing the copolymer may beany suitable conventionally known method. For example, a farnesenemonomer may be polymerized with an isoprene monomer in a solvent using aZiegler-based catalyst, a metallocene-based catalyst or ananion-polymerizable active metal, if required, in the presence of apolar compound.

Examples of the anion-polymerizable active metal include alkali metalssuch as lithium, sodium and potassium; alkali earth metals such asberyllium, magnesium, calcium, strontium and barium; andlanthanoid-based rare earth metals such as lanthanum and neodymium.Among these active metals, preferred are alkali metals and alkali earthmetals, and more preferred are alkali metals. The alkali metals are morepreferably used in the form of an organic alkali metal compound.

Specific examples of the organic alkali metal compound include organicmonolithium compounds such as methyl lithium, ethyl lithium, n-butyllithium, sec-butyl lithium, t-butyl lithium, hexyl lithium, phenyllithium and stilbene lithium; polyfunctional organic lithium compoundssuch as dilithiomethane, dilithionaphthalene, 1,4-dilithiobutane,1,4-dilithio-2-ethyl cyclohexane and 1,3,5-trilithiobenzene; and sodiumnaphthalene and potassium naphthalene. Among these organic alkali metalcompounds, preferred are organic lithium compounds, and more preferredare organic monolithium compounds. The amount of the organic alkalimetal compound used may be appropriately determined according to amolecular weight of the farnesene polymer as required, and is preferablyfrom 0.01 to 3 parts by mass on the basis of 100 parts by mass offarnesene.

The organic alkali metal compound may be used in the form of an organicalkali metal amide by allowing a secondary amine such as dibutyl amine,dihexyl amine and dibenzyl amine to react therewith.

Examples of the solvent used in the solution polymerization includealiphatic hydrocarbons such as n-butane, n-pentane, isopentane,n-hexane, n-heptane and isooctane; alicyclic hydrocarbons such ascyclopentane, cyclohexane and methyl cyclopentane; and aromatichydrocarbons such as benzene, toluene and xylene.

The polar compound may be used in the anion polymerization forcontrolling a microstructure or a random structure of a moiety derivedfrom farnesene or a moiety derived from isoprene without causingdeactivation of the reaction. Examples of the polar compound includeether compounds such as dibutyl ether, diethyl ether, tetrahydrofuran,dioxane and ethylene glycol diethyl ether; pyridine; tertiary aminessuch as tetramethyl ethylenediamine and trimethylamine; and alkali metalalkoxides such as potassium-t-butoxide; and phosphine compounds. Thepolar compound is preferably used in an amount of from 0.01 to 1,000 molequivalent on the basis of the organic alkali metal compound.

The copolymer according to the present invention is preferably producedby conducting an anionic polymerization in the presence of an organicmetal initiator such as the above organic alkali metal compounds fromthe viewpoint of readily controlling a molecular weight distribution ofthe resulting copolymer within the aforementioned range.

The temperature used in the above polymerization reaction is usuallyfrom −80 to 150° C., preferably from 0 to 100° C. and more preferablyfrom 10 to 90° C. The polymerization method may be either a batch methodor a continuous method. The farnesene and isoprene are respectivelysupplied to the reaction solution in a continuous or intermittent mannersuch that the compositional ratio of the farnesene and isoprene in thepolymerization system falls within a specific range, or a mixture of thefarnesene and isoprene which has been previously prepared such that acompositional ratio of these compounds is controlled to a specific rangeis supplied to the reaction solution, whereby it is possible to producea random copolymer. Alternatively, the farnesene and isoprene aresequentially polymerized in the reaction solution such that acompositional ratio of these compounds in the polymerization system iscontrolled to a specific range, whereby it is possible to produce ablock copolymer.

The polymerization reaction may be stopped by adding an alcohol such asmethanol and isopropanol as a terminating reagent to the reactionsystem. The resulting polymerization reaction solution may be pouredinto a poor solvent such as methanol to precipitate the copolymer.Alternatively, the polymerization reaction solution may be washed withwater, and then a solid is separated therefrom and dried to isolate thecopolymer therefrom.

{Modified Copolymer}

The copolymer according to the present invention may be used in amodified form. Examples of a functional group used for modifying thecopolymer include an amino group, an alkoxysilyl group, a hydroxylgroup, an epoxy group, a carboxyl group, a carbonyl group, a mercaptogroup, an isocyanate group and an acid anhydride group.

As the method of producing the modified copolymer, there may be used,for example, the method in which before adding the terminating reagent,a coupling reagent such as tin tetrachloride, tetrachlorosilane,dimethyl dichlorosilane, dimethyl diethoxysilane, tetramethoxysilane,tetraethoxysilane, 3-aminopropyl triethoxysilane,tetraglycidyl-1,3-bisaminomethyl cyclohexane and 2,4-tolylenediisocyanate which are capable of reacting with an active end of thepolymer chain, a chain end-modifying reagent such as4,4′-bis(diethylamino)benzophenone and N-vinyl pyrrolidone, or the othermodifying reagent as described in JP 2011-132298A is added to thepolymerization reaction system. Furthermore, the isolated copolymer maybe grafted with maleic anhydride or the like.

In the modified copolymer, the site of the polymer into which thefunctional group is introduced may be either a chain end or a side chainof the polymer. In addition, these functional groups may be used aloneor in combination of any two or more thereof. The modifying reagent maybe used in an amount of from 0.01 to 100 mol equivalent and preferablyfrom 0.01 to 10 mol equivalent on the basis of the organic alkali metalcompound.

[Rubber Composition]

The first rubber composition according to the present invention includes(A) the above copolymer according to the present invention; (B) a rubbercomponent; and (C) carbon black.

The second rubber composition according to the present inventionincludes (A) the above copolymer according to the present invention; (B)a rubber component; and (D) silica.

The third rubber composition according to the present invention includes(A) the above copolymer according to the present invention; (B) a rubbercomponent; (C) carbon black; and (D) silica.

<Rubber Component (B)>

Examples of the rubber component (B) used herein include a naturalrubber, a styrene-butadiene rubber (hereinafter also referred to merelyas “SBR”), a butadiene rubber, an isoprene rubber, a butyl rubber, ahalogenated butyl rubber, an ethylene propylene diene rubber, anethylene propylene diene rubber, a butadiene acrylonitrile copolymerrubber and a chloroprene rubber. Of these rubbers, preferred are SBR, anatural rubber, a butadiene rubber and an isoprene rubber, and morepreferred are SBR and a natural rubber. These rubbers may be used aloneor in combination of any two or more thereof.

[Natural Rubber]

Examples of the natural rubber used as the rubber component (B) in thepresent invention include natural rubbers ordinarily used in tireindustries, e.g., TSR such as SMR, SIR and STR; and RSS, etc.;high-purity natural rubbers; and modified natural rubbers such asepoxidized natural rubbers, hydroxylated natural rubbers, hydrogenatednatural rubbers and grafted natural rubbers. Among these naturalrubbers, STR20, SMR20 and RSS #3 are preferred from the viewpoints of aless variation in quality and a good availability. These natural rubbersmay be used alone or in combination of any two or more thereof.

[Synthetic Rubber]

Examples of a synthetic rubber used as the rubber component (B) in thepresent invention include SBR, a butadiene rubber, an isoprene rubber, abutyl rubber, a halogenated butyl rubber, an ethylene propylene dienerubber, a butadiene acrylonitrile copolymer rubber and a chloroprenerubber. Of these rubbers, preferred are SBR, an isoprene rubber and abutadiene rubber.

(SBR)

As SBR, there may be used those generally used in the applications oftires. More specifically, the SBR preferably has a styrene content offrom 0.1 to 70% by mass and more preferably from 5 to 50% by mass. Also,the SBR preferably has a vinyl content of from 0.1 to 60% by mass andmore preferably from 0.1 to 55% by mass.

The weight-average molecular weight (Mw) of the SBR is preferably from100,000 to 2,500,000, more preferably from 150,000 to 2,000,000 andstill more preferably from 200,000 to 1,500,000. When the weight-averagemolecular weight of the SBR falls within the above-specified range, theresulting rubber composition can be enhanced in both processability andmechanical strength. Meanwhile, in the present specification, theweight-average molecular weight is the value measured by the methoddescribed below in Examples.

The glass transition temperature (Tg) of the SBR used in the presentinvention as measured by differential thermal analysis is preferablyfrom −95° C. to 0° C. and more preferably from −95° C. to −5° C. Whenadjusting Tg of the SBR to the above-specified range, it is possible tosuppress increase in viscosity of the SBR and enhance a handlingproperty thereof.

<<Method for Producing SBR>>

The SBR usable in the present invention may be produced bycopolymerizing styrene and butadiene. The production method of the SBRis not particularly limited, and the SBR may be produced by any of anemulsion polymerization method, a solution polymerization method, avapor phase polymerization method and a bulk polymerization method. Ofthese polymerization methods, preferred are an emulsion polymerizationmethod and a solution polymerization method.

(i) Emulsion-Polymerized Styrene-Butadiene Rubber (E-SBR)

E-SBR may be produced by an ordinary emulsion polymerization method. Forexample, a predetermined amount of a styrene monomer and a predeterminedamount of a butadiene monomer are emulsified and dispersed in thepresence of an emulsifying reagent, and then the resulting emulsion issubjected to emulsion polymerization using a radical polymerizationinitiator.

As the emulsifying reagent, there may be used, for example, a long-chainfatty acid salt having 10 or more carbon atoms or a rosinic acid salt.Specific examples of the emulsifying reagent include potassium salts andsodium salts of fatty acids such as capric acid, lauric acid, myristicacid, palmitic acid, oleic acid and stearic acid.

As a dispersant for the above emulsion polymerization, there may beusually used water. The dispersant may also contain a waster-solubleorganic solvent such as methanol and ethanol unless the use of such anorganic solvent gives any adverse influence on stability upon thepolymerization.

Examples of the radical polymerization initiator include persulfatessuch as ammonium persulfate and potassium persulfate, organic peroxidesand hydrogen peroxide.

In order to suitably adjust a molecular weight of the obtained E-SBR,there may be used a chain transfer reagent. Examples of the chaintransfer reagent include mercaptans such as t-dodecyl mercaptan andn-dodecyl mercaptan; and carbon tetrachloride, thioglycolic acid,diterpene, terpinolene, γ-terpinene and an α-methyl styrene dimer.

The temperature used upon the emulsion polymerization may beappropriately determined according to the kind of radical polymerizationinitiator used therein, and is usually preferably from 0 to 100° C. andmore preferably from 0 to 60° C. The polymerization method may be eithera continuous polymerization method or a batch polymerization method. Thepolymerization reaction may be stopped by adding a terminating reagentto the reaction system.

Examples of the terminating reagent include amine compounds such asisopropyl hydroxyl amine, diethyl hydroxyl amine and hydroxyl amine;quinone-based compounds such as hydroquinone and benzoquinone; andsodium nitrite.

After stopping the polymerization reaction, an antioxidant may be addedto the polymerization reaction system, if required. Furthermore, afterstopping the polymerization reaction, unreacted monomers may be removedfrom the resulting latex, if required. Thereafter, the obtained polymeris coagulated by adding a salt such as sodium chloride, calcium chlorideand potassium chloride as a coagulant thereto and, if required, whileadjusting a pH value of the coagulation system by adding an acid such asnitric acid and sulfuric acid thereto, and then the dispersing solventis separated from the reaction solution to recover the polymer as acrumb. The thus recovered crumb is washed with water and dehydrated, andthen dried using a band dryer or the like to obtain E-SBR. Meanwhile,upon coagulating the polymer, the latex may be previously mixed, ifrequired, with an extender oil in the form of an emulsified dispersionto recover the polymer in the form of an oil-extended rubber.

(ii) Solution-Polymerized Styrene-Butadiene Rubber (S-SBR)

S-SBR may be produced by an ordinary solution polymerization method. Forexample, styrene and butadiene are polymerized in a solvent using ananion-polymerizable active metal, if required, in the presence of apolar compound.

Examples of the anion-polymerizable active metal include alkali metalssuch as lithium, sodium and potassium; alkali earth metals such asberyllium, magnesium, calcium, strontium and barium; andlanthanoid-based rare earth metals such as lanthanum and neodymium.Among these active metals, preferred are alkali metals and alkali earthmetals, and more preferred are alkali metals. The alkali metals are morepreferably used in the form of an organic alkali metal compound.

Specific examples of the organic alkali metal compound include organicmonolithium compounds such as n-butyl lithium, sec-butyl lithium,t-butyl lithium, hexyl lithium, phenyl lithium and stilbene lithium;polyfunctional organic lithium compounds such as dilithiomethane,1,4-dilithiobutane, 1,4-dilithio-2-ethyl cyclohexane and1,3,5-trilithiobenzene; and sodium naphthalene and potassiumnaphthalene. Among these organic alkali metal compounds, preferred areorganic lithium compounds, and more preferred are organic monolithiumcompounds. The amount of the organic alkali metal compound used may beappropriately determined according to a molecular weight of S-SBR asrequired.

The organic alkali metal compound may be used in the form of an organicalkali metal amide by allowing a secondary amine such as dibutyl amine,dihexyl amine and dibenzyl amine to react therewith.

Examples of the polar compound include ether compounds such as dibutylether, diethyl ether, tetrahydrofuran, dioxane and ethylene glycoldiethyl ether; pyridine; tertiary amines such as tetramethylethylenediamine and trimethylamine; and alkali metal alkoxides such aspotassium-t-butoxide; and phosphine compounds. The polar compound ispreferably used in an amount of from 0.01 to 1000 mol equivalent on thebasis of the organic alkali metal compound.

Examples of the solvent include aliphatic hydrocarbons such as n-butane,n-pentane, isopentane, n-hexane, n-heptane and isooctane; alicyclichydrocarbons such as cyclopentane, cyclohexane and methyl cyclopentane;and aromatic hydrocarbons such as benzene and toluene. These solvents ispreferably used in such an amount that a monomer is usually dissolvedtherein at a concentration of from 1 to 50% by mass.

The temperature used in the above polymerization reaction is usuallyfrom −80 to 150° C., preferably from 0 to 100° C. and more preferablyfrom 30 to 90° C. The polymerization method may be either a batch methodor a continuous method. Also, in order to improve a randomcopolymerizability between styrene and butadiene, the styrene andbutadiene are preferably supplied to the reaction solution in acontinuous or intermittent manner such that a compositional ratiobetween the styrene and butadiene in the polymerization system fallswithin a specific range.

The polymerization reaction may be stopped by adding an alcohol such asmethanol and isopropanol as a terminating reagent to the reactionsystem. The polymerization reaction solution obtained after stopping thepolymerization reaction may be directly subjected to drying or steamstripping to remove the solvent therefrom, thereby recovering the S-SBRas aimed. Meanwhile, before removing the solvent, the polymerizationreaction solution may be previously mixed with an extender oil torecover the S-SBR in the form of an oil-extended rubber.

{Modified Styrene-Butadiene Rubber (Modified SBR)}

In the present invention, there may also be used a modified SBR producedby introducing a functional group into SBR. Examples of the functionalgroup to be introduced into SBR include an amino group, an alkoxysilylgroup, a hydroxyl group, an epoxy group and a carboxyl group.

As the method of producing the modified SBR, there may be used, forexample, the method in which before adding the terminating reagent, acoupling reagent such as tin tetrachloride, tetrachlorosilane, dimethyldichlorosilane, dimethyl diethoxysilane, tetramethoxysilane,tetraethoxysilane, 3-aminopropyl triethoxysilane,tetraglycidyl-1,3-bisaminomethyl cyclohexane and 2,4-tolylenediisocyanate which are capable of reacting with an active end of thepolymer chain, a chain end-modifying reagent such as4,4′-bis(diethylamino)benzophenone and N-vinyl pyrrolidone, or the othermodifying reagent as described in JP 2011-132298A is added to thepolymerization reaction system.

In the modified SBR, the site of the polymer into which the functionalgroup is introduced may be either a chain end or a side chain of thepolymer.

(Isoprene Rubber)

The isoprene rubber may be a commercially available isoprene rubberwhich may be obtained, for example, by the polymerization using aZiegler-based catalyst such as titanium tetrahalide-trialkylaluminum-based catalysts, diethyl aluminum chloride-cobalt-basedcatalysts, trialkyl aluminum-boron trifluoride-nickel-based catalystsand diethyl aluminum chloride-nickel-based catalysts; a lanthanoid-basedrare earth metal catalyst such as triethyl aluminum-organic acidneodymium salt-Lewis acid-based catalysts; or an organic alkali metalcompound as used similarly for production of the S-SBR. Among theseisoprene rubbers, preferred are isoprene rubbers obtained by thepolymerization using the Ziegler-based catalyst because of a high cisisomer content thereof. In addition, there may also be used thoseisoprene rubbers having an ultrahigh cis isomer content which areproduced using the lanthanoid-based rare earth metal catalyst.

The isoprene rubber has a vinyl content of 50% by mass or less,preferably 40% by mass or less, and more preferably 30% by mass or less.When the vinyl content of the isoprene rubber is more than 50% by mass,the resulting rubber composition tends to be deteriorated in rollingresistance performance. The lower limit of the vinyl content of theisoprene rubber is not particularly limited. The glass transitiontemperature of the isoprene rubber may vary depending upon the vinylcontent thereof, and is preferably −20° C. or lower and more preferably−30° C. or lower.

The weight-average molecular weight of the isoprene rubber is preferablyfrom 90,000 to 2,000,000 and more preferably from 150,000 to 1,500,000.When the weight-average molecular weight of the isoprene rubber fallswithin the above-specified range, the resulting rubber composition canexhibit a good processability and a good mechanical strength.

The isoprene rubber may partially have a branched structure or maypartially contain a polar functional group by using a polyfunctionaltype modifying reagent, for example, a modifying reagent such as tintetrachloride, silicon tetrachloride, an alkoxysilane containing anepoxy group in a molecule thereof, and an amino group-containingalkoxysilane.

(Butadiene Rubber)

The butadiene rubber may be a commercially available butadiene rubberwhich may be obtained, for example, by the polymerization using aZiegler-based catalyst such as titanium tetrahalide-trialkylaluminum-based catalysts, diethyl aluminum chloride-cobalt-basedcatalysts, trialkyl aluminum-boron trifluoride-nickel-based catalystsand diethyl aluminum chloride-nickel-based catalysts; a lanthanoid-basedrare earth metal catalyst such as triethyl aluminum-organic acidneodymium salt-Lewis acid-based catalysts; or an organic alkali metalcompound as used similarly for production of the S-SBR. Among thesebutadiene rubbers, preferred are butadiene rubbers obtained by thepolymerization using the Ziegler-based catalyst because of a high cisisomer content thereof. In addition, there may also be used thosebutadiene rubbers having an ultrahigh cis isomer content which areproduced using the lanthanoid-based rare earth metal catalyst.

The butadiene rubber has a vinyl content of 50% by mass or less,preferably 40% by mass or less, and more preferably 30% by mass or less.When the vinyl content of the butadiene rubber is more than 50% by mass,the resulting rubber composition tends to be deteriorated in rollingresistance performance. The lower limit of the vinyl content of thebutadiene rubber is not particularly limited. The glass transitiontemperature of the butadiene rubber may vary depending upon the vinylcontent thereof, and is preferably −40° C. or lower and more preferably−50° C. or lower.

The weight-average molecular weight of the butadiene rubber ispreferably from 90,000 to 2,000,000, more preferably from 150,000 to1,500,000 and still more preferably from 250,000 to 800,000. When theweight-average molecular weight of the butadiene rubber falls within theabove-specified range, the resulting rubber composition can exhibit agood processability and a good mechanical strength.

The butadiene rubber may partially have a branched structure or maypartially contain a polar functional group by using a polyfunctionaltype modifying reagent, for example, a modifying reagent such as tintetrachloride, silicon tetrachloride, an alkoxysilane containing anepoxy group in a molecule thereof, and an amino group-containingalkoxysilane.

As the synthetic rubber other than the SBR, the isoprene rubber and thebutadiene rubber, there may be used one or more rubbers selected fromthe group consisting of a butyl rubber, a halogenated butyl rubber, anethylene propylene diene rubber, a butadiene acrylonitrile copolymerrubber and a chloroprene rubber. The method of producing these rubbersis not particularly limited, and any suitable commercially availablesynthetic rubbers may also be used in the present invention.

In the present invention, when using the rubber component (B) incombination with the aforementioned copolymer (A), it is possible toimprove a processability of the resulting rubber composition, adispersibility of carbon black, silica, etc., therein and a rollingresistance performance thereof.

When using a mixture of two or more kinds of synthetic rubbers, thecombination of the synthetic rubbers may be optionally selected unlessthe effects of the present invention are adversely influenced. Also,various properties of the resulting rubber composition such as a rollingresistance performance and a wear resistance may be appropriatelycontrolled by selecting a suitable combination of the synthetic rubbers.

Meanwhile, the method for producing the rubber used as the rubbercomponent (B) in the present invention is not particularly limited, andany commercially available product may also be used as the rubber.

The rubber composition preferably contains the above copolymer (A) in anamount of from 0.1 to 100 parts by mass, more preferably from 0.5 to 50parts by mass and still more preferably from 1 to 30 parts by mass onthe basis of 100 parts by mass of the above rubber component (B) fromthe viewpoint of enhancing a rolling resistance performance and a wearresistance of the rubber composition.

<Carbon Black (C)>

Examples of the carbon black (C) usable in the present invention includecarbon blacks such as furnace black, channel black, thermal black,acetylene black and Ketjen black. Of these carbon blacks, from theviewpoints of a high curing rate and an improved mechanical strength ofthe rubber composition, preferred is furnace black.

Examples of commercially available products of the furnace black include“DIABLACK” available from Mitsubishi Chemical Corp., and “SEAST”available from Tokai Carbon Co., Ltd. Examples of commercially availableproducts of the acetylene black include “DENKABLACK” available fromDenki Kagaku Kogyo K.K. Examples of commercially available products ofthe Ketjen black include “ECP600JD” available from Lion Corp.

The carbon black (C) may be subjected to an acid treatment with nitricacid, sulfuric acid, hydrochloric acid or a mixed acid thereof or may besubjected to a heat treatment in the presence of air for conducting asurface oxidation treatment thereof, from the viewpoint of improving awettability or a dispersibility of the carbon black (C) in the copolymer(A) and the rubber component (B). In addition, from the viewpoint ofimproving a mechanical strength of the rubber composition of the presentinvention, the carbon black may be subjected to a heat treatment at atemperature of from 2,000 to 3,000° C. in the presence of agraphitization catalyst. As the graphitization catalyst, there may besuitably used boron, boron oxides (such as, for example, B₂O₂, B₂O₃,B₄O₃ and B₄O₅), oxo acids of boron (such as, for example, orthoboricacid, metaboric acid and tetraboric acid) and salts thereof, boroncarbides (such as, for example, B₄C and B₆C), boron nitride (such as BN)and other boron compounds.

The average particle size of the carbon black (C) may be controlled bypulverization or the like. In order to pulverize the carbon black (C),there may be used a high-speed rotary mill (such as a hammer mill, a pinmil and a cage mill) or various ball mills (such as a rolling mill, avibration mill and a planetary mill), a stirring mill (such as a beadsmill, an attritor, a flow tube mill and an annular mill) or the like.

The carbon black (C) preferably has an average particle size of from 5to 100 nm and more preferably from 10 to 80 nm from the viewpoint ofimproving a dispersibility in the rubber composition and a mechanicalstrength of the rubber composition.

Meanwhile, the average particle size of the carbon black (C) may bedetermined by calculating an average value of diameters of carbon blackparticles measured using a transmission type electron microscope.

In the rubber composition of the present invention, the carbon black (C)is preferably compounded in an amount of from 0.1 to 150 pars by mass,more preferably from 2 to 150 parts by mass, still more preferably from5 to 90 parts by mass and even still more preferably from 20 to 80 partsby mass on the basis of 100 parts by mass of the rubber component (B).When the amount of the carbon black (C) compounded falls within theabove-specified range, the resulting rubber composition is not onlyexcellent in mechanical strength, hardness and processability, but alsoexhibits a good dispersibility of the carbon black (C) therein.

<Silica (D)>

Examples of the silica (D) include wet silica (hydrous silicic acid),dry silica (anhydrous silicic acid), calcium silicate and aluminumsilicate. Of these silicas, from the viewpoint of further enhancing aprocessability, a mechanical strength and a wear resistance of theresulting rubber composition, preferred is wet silica. These silicas maybe used alone or in combination of any two or more thereof.

The silica (D) preferably has an average particle size of from 0.5 to200 nm, more preferably from 5 to 150 nm, still more preferably from 10to 100 nm and even still more preferably from 10 to 60 nm from theviewpoint of enhancing a processability, a rolling resistanceperformance, a mechanical strength and a wear resistance of theresulting rubber composition.

Meanwhile, the average particle size of the silica (D) may be determinedby calculating an average value of diameters of silica particlesmeasured using a transmission type electron microscope.

In the rubber composition of the present invention, the silica (D) ispreferably compounded in an amount of from 0.1 to 150 pars by mass, morepreferably from 0.5 to 130 parts by mass, still more preferably from 5to 100 parts by mass and even still more preferably from 5 to 95 partsby mass on the basis of 100 parts by mass of the rubber component (B).When the amount of the silica (D) compounded falls within theabove-specified range, the resulting rubber composition can be enhancedin processability, rolling resistance performance, mechanical strengthand wear resistance.

The rubber composition according to the present invention morepreferably contains the above copolymer (A), carbon black (C) and silica(D) in amounts of from 0.1 to 100 parts by mass, from 0.1 to 150 partsby mass and from 0.1 to 150 parts by mass, respectively, on the basis of100 parts by mass of the above rubber component (B).

<Optional Components>

(Silane Coupling Reagent)

The rubber composition according to the present invention alsopreferably contains a silane coupling reagent. As the silane couplingreagent, there may be used a sulfide-based compound, a mercapto-basedcompound, a vinyl-based compound, an amino-based compound, aglycidoxy-based compound, a nitro-based compound, a chloro-basedcompound, etc.

Examples of the sulfide-based compound includebis(3-triethoxysilylpropyl)tetrasulfide,bis(2-triethoxysilylethyl)tetrasulfide,bis(3-trimethoxysilylpropyl)tetrasulfide,bis(2-trimethoxysilylethyl)tetrasulfide,bis(3-triethoxysilylpropyl)trisulfide,bis(3-trimethoxysilylpropyptrisulfide,bis(3-triethoxysilylpropyl)disulfide,bis(3-trimethoxysilylpropyl)disulfide,3-trimethoxysilylpropyl-N,N-dimethyl thiocarbamoyl tetrasulfide,3-triethoxysilylpropyl-N,N-dimethyl thiocarbamoyl tetrasulfide,2-trimethoxysilylethyl-N,N-dimethyl thiocarbamoyl tetrasulfide,3-trimethoxysilylpropyl benzothiazole tetrasulfide,3-triethoxysilylpropyl benzothiazole tetrasulfide,3-triethoxysilylpropyl methacrylate monosulfide and3-trimethoxysilylpropyl methacrylate monosulfide.

Examples of the mercapto-based compound include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyl triethoxysilane, 2-mercaptoethyltrimethoxysilane and 2-mercaptoethyl triethoxysilane.

Examples of the vinyl-based compound include vinyl triethoxysilane andvinyl trimethoxysilane.

Examples of the amino-based compound include 3-aminopropyltriethoxysilane, 3-aminopropyl trimethoxysilane,3-(2-aminoethyl)aminopropyl triethoxysilane and3-(2-aminoethyl)aminopropyl trimethoxysilane.

Examples of the glycidoxy-based compound include γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyl trimethoxysilane, γ-glycidoxypropylmethyl diethoxysilane and γ-glycidoxypropyl methyl dimethoxysilane.

Examples of the nitro-based compound include 3-nitropropyltrimethoxysilane and 3-nitropropyl triethoxysilane.

Examples of the chloro-based compound include 3-chloropropyltrimethoxysilane, 3-chloropropyl triethoxysilane, 2-chloroethyltrimethoxysilane and 2-chloroethyl triethoxysilane.

These silane coupling reagents may be used alone or in combination ofany two or more thereof. Of these silane coupling gents, from theviewpoints of a large addition effect and low costs, preferred arebis(3-triethoxysilylpropyl)disulfide,bis(3-triethoxysilylpropyl)tetrasulfide and 3-mercaptopropyltrimethoxysilane.

The content of the silane coupling reagent in the rubber composition ispreferably from 0.1 to 30 parts by mass, more preferably from 0.5 to 20parts by mass and still more preferably from 1 to 15 parts by mass onthe basis of 100 parts by mass of the silica (D). When the content ofthe silane coupling reagent in the rubber composition falls within theabove-specified range, the resulting rubber composition can be enhancedin dispersibility, coupling effect, reinforcing property and wearresistance.

(Other Fillers)

For the purposes of enhancing a mechanical strength of the rubbercomposition, improving various properties such as a heat resistance anda weathering resistance thereof, controlling a hardness thereof, andfurther improving economy by adding an extender thereto, the rubbercomposition according to the present invention may further contain afiller other than the carbon black (C) and silica (D), if required.

The filler other than the carbon black (C) and silica (D) may beappropriately selected according to the applications of the obtainedrubber composition. For example, as the filler, there may be used one ormore fillers selected from the group consisting of organic fillers, andinorganic fillers such as clay, talc, mica, calcium carbonate, magnesiumhydroxide, aluminum hydroxide, barium sulfate, titanium oxide, glassfibers, fibrous fillers and glass balloons. The content of the abovefiller in the rubber composition of the present invention, if compoundedtherein, is preferably from 0.1 to 120 parts by mass, more preferablyfrom 5 to 90 parts by mass and still more preferably from 10 to 80 partsby mass on the basis of 100 parts by mass of the rubber component (B).When the content of the filler in the rubber composition falls withinthe above-specified range, the resulting rubber composition can befurther improved in mechanical strength.

The rubber composition according to the present invention may alsocontain, if required, a softening reagent for the purpose of improving aprocessability, a flowability or the like of the resulting rubbercomposition unless the effects of the present invention are adverselyinfluenced. Examples of the softening reagent include a process oil suchas a silicone oil, an aroma oil, TDAE (treated distilled aromaticextracts), MES (mild extracted solvates), RAE (residual aromaticextracts), a paraffin oil and a naphthene oil; a resin component such asaliphatic hydrocarbon resins, alicyclic hydrocarbon resins, C9-basedresins, rosin-based resins, coumarone-indene-based resins andphenol-based resins; and a liquid polymer such as a low-molecular weightpolybutadiene, a low-molecular weight polyisoprene, a low-molecularweight styrene-butadiene copolymer and a low-molecular weightstyrene-isoprene copolymer. Meanwhile, the above copolymers may be inthe form of either a block copolymer or a random copolymer. The liquidpolymer preferably has a weight-average molecular weight of from 500 to100,000 from the viewpoint of a good processability of the resultingrubber composition. The above process oil, resin component or liquidpolymer as a softening reagent is preferably compounded in the rubbercomposition of the present invention in an amount of less than 50 partsby mass on the basis of 100 parts by mass of the rubber component (B).

The rubber composition according to the present invention may alsocontain a homopolymer of β-farnesene unless the effects of the presentinvention are adversely influenced. The content of the homopolymer ofβ-farnesene in the rubber composition, if compounded therein, ispreferably less than 50 parts by mass on the basis of 100 parts by massof the rubber component (B).

The rubber composition according to the present invention may alsocontain, if required, one or more additives selected from the groupconsisting of an antioxidant, an oxidation inhibitor, a wax, alubricant, a light stabilizer, a scorch retarder, a processing aid, acolorant such as pigments and coloring matters, a flame retardant, anantistatic reagent, a delustering reagent, an anti-blocking reagent, anultraviolet absorber, a release reagent, a foaming reagent, anantimicrobial reagent, a mildew-proofing reagent and a perfume, for thepurposes of improving a weathering resistance, a heat resistance, anoxidation resistance or the like of the resulting rubber composition,unless the effects of the present invention are adversely influenced.

Examples of the oxidation inhibitor include hindered phenol-basedcompounds, phosphorus-based compounds, lactone-based compounds andhydroxyl-based compounds.

Examples of the antioxidant include amine-ketone-based compounds,imidazole-based compounds, amine-based compounds, phenol-basedcompounds, sulfur-based compounds and phosphorus-based compounds.

The rubber composition of the present invention is preferably used inthe from of a crosslinked product produced by adding a crosslinkingreagent thereto. Examples of the crosslinking reagent include sulfur andsulfur compounds, oxygen, organic peroxides, phenol resins and aminoresins, quinone and quinone dioxime derivatives, halogen compounds,aldehyde compounds, alcohol compounds, epoxy compounds, metal halidesand organic metal halides, and silane compounds. Among thesecrosslinking reagents, preferred are sulfur and sulfur compounds. Thesecrosslinking reagents may be used alone or in combination of any two ormore thereof. The crosslinking reagent is preferably compounded in therubber composition in an amount of from 0.1 to 10 parts by mass on thebasis of 100 parts by mass of the rubber component (B).

When using sulfur as the crosslinking reagent, a vulcanization aid or avulcanization accelerator is preferably used in combination with thecrosslinking reagent.

Examples of the vulcanization aid include fatty acids such as stearicacid and metal oxides such as zinc oxide.

Examples of the vulcanization accelerator include guanidine-basedcompounds, sulfene amide-based compounds, thiazole-based compounds,thiuram-based compounds, thiourea-based compounds, dithiocarbamicacid-based compounds, aldehyde-amine-based compounds oraldehyde-ammonia-based compounds, imidazoline-based compounds andxanthate-based compounds. These vulcanization aids or vulcanizationaccelerators may be used alone or in combination of any two or morethereof. The vulcanization aid or vulcanization accelerator ispreferably compounded in the rubber composition of the present inventionin an amount of from 0.1 to 15 parts by mass on the basis of 100 partsby mass of the rubber component (B).

The method for producing the rubber composition of the present inventionis not particularly limited, and any suitable method may be used in thepresent invention as long as the respective components are uniformlymixed with each other. The method of uniformly mixing the respectivecomponents may be carried out, for example, using a closed type kneaderof a contact type or a meshing type such a kneader rudder, a Brabender,a Banbury mixer and an internal mixer, a single-screw extruder, atwin-screw extruder, a mixing roll, a roller or the like in atemperature range of usually from 70 to 270° C.

[Tire]

The tire according to the present invention is produced by using therubber composition according to the present invention at least as a partthereof, and therefore can exhibit a good mechanical strength and anexcellent rolling resistance performance.

EXAMPLES

The present invention will be described in more detail below byreferring to the following examples. It should be noted, however, thatthe following examples are only illustrative and not intended to limitthe invention thereto.

The respective components used in the following Examples and ComparativeExamples are as follows.

Copolymer (A):

Copolymers (A-1) to (A-4) obtained in Production Examples 1 to 4,respectively.

Rubber Component (B):

Natural rubber “STR20” (natural rubber from Thailand)

Styrene-butadiene rubber “JSR1500” (available from JSR Corp.)

Butadiene rubber “BR-01” (available from JSR Corp.)

-   -   Weight-average molecular weight=550,000    -   Cis isomer content=95% by mass        Carbon Black (C-1):

“DIABLACK H” available from Mitsubishi Chemical Corp.; average particlesize: 30 nm

Carbon Black (C-2):

“DIABLACK I” available from Mitsubishi Chemical Corp.; average particlesize: 20 nm

Carbon Black (C-3):

“SEAST V” available from Tokai Carbon Co., Ltd.; average particle size:60 nm

Silica (D-1):

“ULTRASIL7000GR” available from Evonik Degussa Japan Co., Ltd.; wetsilica; average particle size: 14 nm

Silica (D-2):

“AEROSIL 300” available from Nippon Aerosil Co., Ltd.; dry silica;average particle size: 7 nm

Silica (D-3):

“NIPSIL E-74P” available from Tosoh Silica Corporation; wet silica;average particle size: 74 nm

Polyisoprene:

Polyisoprene obtained in Production Example 5

Homopolymer of β-farnesene:

Homopolymer of β-farnesene obtained in Production Example 6 TDAE:

“VivaTec500” available from H & R Corp.

Silane Coupling Reagent:

“Si75” (available from Evonik Degussa Japan Co., Ltd.)

Stearic Acid:

“LUNAC S-20” (available from Kao Corp.)

Zinc Oxide:

Zinc oxide (available from Sakai Chemical Industry Co., Ltd.)

Antioxidant (1):

“NOCRAC 6C” (available from Ouchi Shinko Chemical Industrial Co., Ltd.)

Antioxidant (2):

“ANTAGE RD” (available from Kawaguchi Chemical Industry Co., Ltd.)

Sulfur:

Sulfur fine powder 200 mesh (available from Tsurumi Chemical IndustryCo., Ltd.)

Vulcanization Accelerator (1):

“NOCCELER NS” (available from Ouchi Shinko Chemical Industrial Co.,Ltd.)

Vulcanization Accelerator (2):

“NOCCELER CZ-G” (available from Ouchi Shinko Chemical Industrial Co.,Ltd.)

Vulcanization Accelerator (3):

“NOCCELER D” (available from Ouchi Shinko Chemical Industrial Co., Ltd.)

Vulcanization Accelerator (4):

“NOCCELER TBT-N” (available from Ouchi Shinko Chemical Industrial Co.,Ltd.)

Production Example 1 Production of β-farnesene/isoprene Random Copolymer(A-1)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 1490 g of cyclohexane as a solvent and 12.4 g ofsec-butyl lithium (in the form of a 10.5% by mass cyclohexane solution)as an initiator. The contents of the reaction vessel were heated to 50°C., and 1500 g of a mixture of isoprene (a) and β-farnesene (b) (whichwas previously prepared by mixing 300 g of isoprene (a) and 1200 g ofβ-farnesene (b) in a cylinder) was added thereto at a rate of 10 mL/min,and the mixture was polymerized for 1 h. The resulting polymerizationreaction solution was treated with methanol and then washed with water.After separating water from the thus washed polymerization reactionsolution, the resulting solution was dried at 70° C. for 12 h, therebyobtaining a β-farnesene/isoprene random copolymer (A-1). Variousproperties of the thus obtained β-farnesene/isoprene random copolymer(A-1) are shown in Table 1.

Production Example 2 Production of β-farnesene/isoprene Random Copolymer(A-2)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 1790 g of cyclohexane as a solvent and 10.9 g ofsec-butyl lithium (in the form of a 10.5% by mass cyclohexane solution)as an initiator. The contents of the reaction vessel were heated to 50°C., and 1200 g of a mixture of isoprene (a) and β-farnesene (b) (whichwas previously prepared by mixing 480 g of isoprene (a) and 720 g ofβ-farnesene (b) in a cylinder) was added thereto at a rate of 10 mL/min,and the mixture was polymerized for 1 h. The resulting polymerizationreaction solution was treated with methanol and then washed with water.After separating water from the thus washed polymerization reactionsolution, the resulting solution was dried at 70° C. for 12 h, therebyobtaining a β-farnesene/isoprene random copolymer (A-2). Variousproperties of the thus obtained β-farnesene/isoprene random copolymer(A-2) are shown in Table 1.

Production Example 3 Production of β-farnesene/isoprene Block Copolymer(A-3)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 2090 g of cyclohexane as a solvent and 8.2 g ofsec-butyl lithium (in the form of a 10.5% by mass cyclohexane solution)as an initiator. The contents of the reaction vessel were heated to 50°C., and 360 g of isoprene (a) was added thereto at a rate of 10 mL/min,and the mixture was polymerized for 1 h. Successively, 540 g ofβ-farnesene (b) was added to the polymerization reaction solution at arate of 10 mL/min, and the mixture was further polymerized for 1 h. Theresulting polymerization reaction solution was treated with methanol andthen washed with water. After separating water from the thus washedpolymerization reaction solution, the resulting solution was dried at70° C. for 12 h, thereby obtaining a β-farnesene/isoprene blockcopolymer (A-3). Various properties of the thus obtainedβ-farnesene/isoprene block copolymer (A-3) are shown in Table 1.

Production Example 4 Production of β-farnesene/isoprene/β-farneseneBlock Copolymer (A-4)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 1670 g of cyclohexane as a solvent and 10.2 g ofsec-butyl lithium (in the form of a 10.5% by mass cyclohexane solution)as an initiator. The contents of the reaction vessel were heated to 50°C., and 336 g of β-farnesene (b) was added thereto at a rate of 10mL/min, and the mixture was polymerized for 1 h. Successively, 448 g ofisoprene (a) was added to the polymerization reaction solution at a rateof 10 mL/min, and the mixture was further polymerized for 1 h.Successively, 336 g of β-farnesene (b) was added to the polymerizationreaction solution at a rate of 10 mL/min, and the mixture was furtherpolymerized for 1 h. The resulting polymerization reaction solution wastreated with methanol and then washed with water. After separating waterfrom the thus washed polymerization reaction solution, the resultingsolution was dried at 70° C. for 12 h, thereby obtaining aβ-farnesene/isoprene/β-farnesene block copolymer (A-4). Variousproperties of the thus obtained β-farnesene/isoprene/β-farnesene blockcopolymer (A-4) are shown in Table 1.

Production Example 5 Production of Polyisoprene

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 600 g of hexane and 44.9 g of n-butyl lithium (inthe form of a 17% by mass hexane solution). The contents of the reactionvessel were heated to 70° C., and 2050 g of isoprene was added thereto,and the mixture was polymerized for 1 h. The resulting polymerizationreaction solution was mixed with methanol and then washed with water.After separating water from the thus washed polymerization reactionsolution, the resulting solution was dried at 70° C. for 12 h, therebyobtaining a polyisoprene having properties as shown in Table 1.

Production Example 6 Production of Homopolymer of β-farnesene

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 274 g of hexane as a solvent and 1.2 g of n-butyllithium (in the form of a 17% by mass hexane solution) as an initiator.The contents of the reaction vessel were heated to 50° C., and 272 g ofp-farnesene was added thereto, and the mixture was polymerized for 1 h.Successively, the resulting polymerization reaction solution was treatedwith methanol and then washed with water. After separating water fromthe thus washed polymerization reaction solution, the resulting solutionwas dried at 70° C. for 12 h, thereby obtaining a homopolymer ofβ-farnesene. Various properties of the thus obtained homopolymer ofβ-farnesene are shown in Table 1.

Meanwhile, the weight-average molecular weight and melt viscosity ofeach of the copolymer (A), polyisoprene and homopolymer of β-farnesenewere measured by the following methods.

(Method of Measuring Weight-Average Molecular Weight)

The weight-average molecular weight (Mw) and the molecular weightdistribution (Mw/Mn) of each of the copolymer (A), polyisoprene andhomopolymer of β-farnesene were measured by GPC (gel permeationchromatography) in terms of a molecular weight of polystyrene as areference standard substance. The measuring devices and conditions areas follows.

-   -   Apparatus: GPC device “GPC8020” available from Tosoh Corp.    -   Separating column: “TSKgelG4000HXL” available from Tosoh Corp.    -   Detector: “RI-8020” available from Tosoh Corp.    -   Eluent: Tetrahydrofuran    -   Eluent flow rate: 1.0 mL/min    -   Sample concentration: 5 mg/10 mL    -   Column temperature: 40° C.        (Method of Measuring Melt Viscosity)

The melt viscosity of each of the copolymer (A), polyisoprene andhomopolymer of β-farnesene was measured at 38° C. using a B-typeviscometer available from Brookfield Engineering Labs. Inc.

TABLE 1 Molecular Weight-average weight Polymerization (a)/{(a) + (b)}molecular distribution Melt viscosity Polymer form (mass %) weight(×10³) Mw/Mn (at 38° C.) (Pa · s) Production Copolymer (A-1) Random 20101 1.1 88 Example 1 Production Copolymer (A-2) Random 40 98 1.05 232Example 2 Production Copolymer (A-3) Block 40 99 1.02 258 Example 3Production Copolymer (A-4) Block 40 96 1.06 293 Example 4 ProductionPolyisoprene — — 32 1.1 74 Example 5 Production Homopolymer — — 140 1.165 Example 6 of β-farnesene

Examples 1 to 13 and Comparative Examples 1 to 8

The copolymer (A), rubber component (B), carbon black (C), silica (D),silane coupling reagent, polyisoprene, TDAE, stearic acid, zinc oxideand antioxidant were charged at respective compounding ratios as shownin Tables 2 to 4 into a closed type Banbury mixer and kneaded togetherfor 6 min such that the initiating temperature was 75° C. and the resintemperature reached 160° C. The resulting mixture was once taken out ofthe mixer, and cooled to room temperature. Next, the mixture was placedin a mixing roll, and after adding sulfur and the vulcanizationaccelerator thereto, the contents of the mixing roll were kneaded at 60°C. for 6 min, thereby obtaining a rubber composition. The Mooneyviscosity of the thus obtained rubber composition was measured by thefollowing method.

In addition, the resulting rubber composition was press-molded (at 145°C. for 20 to 60 min) to prepare a sheet (thickness: 2 mm). The thusprepared sheet was evaluated for a tensile strength at break, DINabrasion loss and a rolling resistance performance by the followingmethods. The results are shown in Tables 2 to 4.

(1) Mooney Viscosity

As an index of a processability of the rubber composition, the Mooneyviscosity (ML1+4) of the rubber composition before being cured wasmeasured at 100° C. according to JIS K 6300. The values of therespective Examples and Comparative Examples shown in Table 2 arerelative values based on 100 as the value of Comparative Example 3. Thevalues of the respective Examples and Comparative Examples shown inTable 3 are relative values based on 100 as the value of ComparativeExample 6. The values of the respective Examples and ComparativeExamples shown in Table 4 are relative values based on 100 as the valueof Comparative Example 8. Meanwhile, the smaller Mooney viscosity valueindicates a more excellent processability.

(2) Tensile Strength at Break

A sheet prepared from the rubber composition produced in the respectiveExamples and Comparative Examples was punched into a JIS No. 3dumbbell-shaped test piece, and the obtained test piece was subjected tomeasurement of a tensile strength at break thereof using a tensiletester available from Instron Corp., according to JIS K 6251. The valuesof the respective Examples and Comparative Examples shown in Table 2 arerelative values based on 100 as the value of Comparative Example 3. Thevalues of the respective Examples and Comparative Examples shown inTable 3 are relative values based on 100 as the value of ComparativeExample 6. The values of the respective Examples and ComparativeExamples shown in Table 4 are relative values based on 100 as the valueof Comparative Example 8. Meanwhile, the larger value indicates a bettertensile strength at break of the rubber composition.

(3) DIN Abrasion Loss

The rubber composition was measured for DIN abrasion loss under a loadof 10 N at an abrasion distance of 40 m according to JIS K 6264. Thevalues of the respective Examples and Comparative Examples shown inTable 2 are relative values based on 100 as the value of ComparativeExample 3. The values of the respective Examples and ComparativeExamples shown in Table 3 are relative values based on 100 as the valueof Comparative Example 6. The values of the respective Examples andComparative Examples shown in Table 4 are relative values based on 100as the value of Comparative Example 8. Meanwhile, the smaller valueindicates a less abrasion loss of the rubber composition.

(4) Rolling Resistance Performance

A sheet prepared from the rubber composition produced in the respectiveExamples and Comparative Examples was cut into a test piece having asize of 40 mm in length×7 mm in width. The thus obtained test piece wassubjected to measurement of tan δ as an index of a rolling resistanceperformance of the rubber composition using a dynamic viscoelasticitymeasuring apparatus available from GABO GmbH under the conditionsincluding a measuring temperature of 60° C., a frequency of 10 Hz, astatic strain of 10% and a dynamic strain of 2%. The values of therespective Examples and Comparative Examples shown in Table 2 arerelative values based on 100 as the value of Comparative Example 3. Thevalues of the respective Examples and Comparative Examples shown inTable 3 are relative values based on 100 as the value of ComparativeExample 6. The values of the respective Examples and ComparativeExamples shown in Table 4 are relative values based on 100 as the valueof Comparative Example 8. Meanwhile, the smaller value indicates anexcellent rolling resistance performance of the rubber composition.

TABLE 2 Comparative Examples Examples 1 2 3 4 1 2 3 Composition (part(s)by mass) Component (A) Copolymer (A-1) 10 Copolymer (A-2) 10 Copolymer(A-3) 10 Copolymer (A-4) 10 Polyisoprene 10 TDAE 10 Component (B)Natural rubber 100 100 100 100 100 100 100 Component (C) Carbon black(C-1) 50 50 50 50 50 50 50 Optional Components Stearic acid 2 2 2 2 2 22 Silane coupling reagent 4 4 4 4 4 4 4 Zinc oxide 3.5 3.5 3.5 3.5 3.53.5 3.5 Antioxidant (1) 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5Vulcanization accelerator (1) 1 1 1 1 1 1 1 Properties Mooney viscosity(relative value) 75 76 78 78 81 75 100 Tensile strength at break(relative value) 92 93 93 96 92 89 100 DIN abrasion loss (relativevalue) 107 107 101 104 107 114 100 Rolling resistance performance (at60° C.; tanδ) 99 103 103 95 110 119 100 (relative value)

The rubber compositions obtained in Examples 1 to 4 exhibited a lowMooney viscosity as compared to that of Comparative Example 3 andtherefore a good processability. Furthermore, the rubber compositionsobtained in Examples 1 to 4 were excellent in rolling resistanceperformance as compared to those of Comparative Examples 1 and 2, andwere also prevented from being deteriorated in mechanical strength andwear resistance.

TABLE 3 Comparative Examples Examples 5 6 7 8 9 4 5 6 Composition(part(s) by mass) Component (A) Copolymer (A-1) 10 Copolymer (A-2) 10 10Copolymer (A-3) 10 Copolymer (A-4) 10 Polyisoprene 10 10 Component (B)Styrene-butadiene rubber 100 100 100 100 100 100 100 100 Component (C)Carbon black (C-1) 25 25 25 25 25 25 Carbon black (C-3) 5 5 Component(D) Silica (D-1) 25 25 25 25 40 25 40 25 Silica (D-2) 10 10 OptionalComponents Silane coupling reagent 2 2 2 2 4 2 4 2 Stearic acid 1 1 1 11 1 1 1 Zinc oxide 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Antioxidant (1) 1 1 11 1 1 1 1 Antioxidant (2) 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.51.5 1.5 Vulcanization accelerator (2) 0.4 0.4 0.4 0.4 0.35 0.4 0.35 0.4Vulcanization accelerator (3) 0.3 0.3 0.3 0.3 0.5 0.3 0.5 0.3Vulcanization accelerator (4) 1.2 1.2 1.2 1.2 1.5 1.2 1.5 1.2 PropertiesMooney viscosity (relative value) 77 76 79 77 88 77 87 100 Tensilestrength at break (relative value) 90 98 90 95 81 90 80 100 DIN abrasionloss (relative value) 110 107 105 105 114 114 114 100 Rolling resistanceperformance (at 60° C.; tanδ) (relative 100 101 101 101 96 104 100 100value)

The rubber compositions obtained in Examples 5 to 8 exhibited a lowMooney viscosity as compared to that of Comparative Example 6 andtherefore a good processability. Furthermore, the rubber compositionsobtained in Examples 5 to 8 were excellent in rolling resistanceperformance as compared to that of Comparative Example 4, and were alsoprevented from being deteriorated in mechanical strength and wearresistance.

From the comparison between Example 9 and Comparative Example 5, it wasconfirmed that when controlling an average particle size of the carbonblack (C) to the range of from 5 to 100 nm and an average particle sizeof the silica (D) to the range of from 0.5 to 200 nm, the resultingrubber composition exhibited a good processability, was prevented frombeing deteriorated in mechanical strength and wear resistance, and wasexcellent in rolling resistance performance.

TABLE 4 Comparative Examples Examples 10 11 12 13 7 8 Composition(part(s) by mass) Component (A) Copolymer (A-1) 10 Copolymer (A-2) 10Copolymer (A-3) 10 Copolymer (A-4) 10 Polyisoprene 10 Component (B)Styrene-butadiene rubber 100 100 100 100 100 100 Component (D) Silica(D-1) 50 50 50 50 50 50 Optional Components Silane coupling reagent 4 44 4 4 4 Stearic acid 1 1 1 1 1 1 Zinc oxide 3.5 3.5 3.5 3.5 3.5 3.5Antioxidant (1) 1 1 1 1 1 1 Antioxidant (2) 1 1 1 1 1 1 Sulfur 1.5 1.51.5 1.5 1.5 1.5 Vulcanization accelerator (2) 0.35 0.35 0.35 0.35 0.350.35 Vulcanization accelerator (3) 0.5 0.5 0.5 0.5 0.5 0.5 Vulcanizationaccelerator (4) 1.5 1.5 1.5 1.5 1.5 1.5 Properties Mooney viscosity(relative value) 88 90 89 90 87 100 Tensile strength at break (relativevalue) 80 81 87 80 80 100 DIN abrasion loss (relative value) 118 117 118116 118 100 Rolling resistance performance (at 60° C.; tanδ) 99 98 98 98104 100 (relative value)

The rubber compositions obtained in Examples 10 to 13 exhibited a lowMooney viscosity as compared to that of Comparative Example 8 andtherefore a good processability. Furthermore, the rubber compositionsobtained in Examples 10 to 13 were excellent in rolling resistanceperformance as compared to that of Comparative Example 7, and were alsoprevented from being deteriorated in mechanical strength and wearresistance.

Examples 14 to 20 and Comparative Examples 9 to 14

The copolymer (A), rubber component (B), carbon black (C), silica (D),homopolymer of β-farnesene, polyisoprene, silane coupling reagent, TDAE,stearic acid, zinc oxide and antioxidant were charged at respectivecompounding ratios as shown in Tables 5 and 6 into a closed type Banburymixer and kneaded together for 6 min such that the initiatingtemperature was 75° C. and the resin temperature reached 160° C. Theresulting mixture was once taken out of the mixer, and cooled to roomtemperature. Next, the mixture was placed in a mixing roll, and afteradding sulfur and the vulcanization accelerator thereto, the contents ofthe mixing roll were kneaded at 60° C. for 6 min, thereby obtaining arubber composition. The Mooney viscosity of the thus obtained rubbercomposition was measured by the above method.

In addition, the resulting rubber composition was press-molded (at 145°C. for 25 to 50 min) to prepare a sheet (thickness: 2 mm). The thusprepared sheet was evaluated for a tensile strength at break and arolling resistance performance by the above methods. The results areshown in Tables 5 and 6.

Furthermore, the rubber compositions obtained in Examples 14 to 19 andComparative Examples 9 to 13 were measured for DIN abrasion loss thereofby the above method. The results are shown in Table 5.

Meanwhile, the values of the Mooney viscosity, tensile strength atbreak, DIN abrasion loss and rolling resistance performance of therespective rubber compositions as shown in Table 5 are relative valuesbased on 100 as each of those values of Comparative Example 13.

Also, the values of the Mooney viscosity, tensile strength at break androlling resistance performance of the respective rubber compositions asshown in Table 6 are relative values based on 100 as each of thosevalues of Comparative Example 14.

TABLE 5 Examples Comparative Examples 14 15 16 17 18 19 9 10 11 12 13Composition (part(s) by mass) Component (A) Copolymer (A-2) 1 10 6 6 630 Homopolymer of β-farnesene 4 Polyisoprene 4 1 10 30 TDAE 4 10Component (B) Natural rubber 100 100 100 100 100 80 100 100 100 80 100Styrene-butadiene rubber Butadiene rubber 20 20 Component (C) Carbonblack (C-2) 45 45 45 45 45 70 45 45 45 70 45 Carbon black (C-3) 10 10Component (D) Silica (D-1) Silica (D-3) 5 5 Silane coupling reagent 0.40.4 Optional Components Stearic acid 2 2 2 2 2 2 2 2 2 2 2 Zinc oxide3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Antioxidant (1) 1 1 1 1 1 11 1 1 1 1 Antioxidant (2) 1 1 1 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization accelerator (1) 1.2 1.2 1.21.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Properties Mooney viscosity (relativevalue) 99 78 77 78 78 85 100 81 76 89 100 Tensile strength at break(relative value) 99 96 95 97 95 74 97 94 89 74 100 DIN abrasion loss(relative value) 100 108 109 106 108 113 100 109 112 113 100 Rollingresistance performance 99 97 87 100 101 141 104 103 106 147 100 (at 60°C.; tanδ) (relative value)

From the comparison between Example 14 and Comparative Example 9, it wasconfirmed that when controlling the amount of the copolymer (A)compounded in the rubber composition to the range of from 0.1 to 100parts by mass based on 100 parts by mass of the rubber component (B),the resulting rubber composition exhibited a good processability, wasprevented from being deteriorated in mechanical strength and wearresistance, and was excellent in rolling resistance performance.

The rubber compositions obtained in Examples 15 to 18 exhibited a lowMooney viscosity as compared to that of Comparative Example 13 andtherefore was improved in processability. Furthermore, the rubbercompositions obtained in Examples 15 to 18 had a tensile strength atbreak and a wear resistance which were almost similar to those ofComparative Example 10 or 11, but were excellent in rolling resistanceperformance as compared to that of Comparative Example 10 or 11, andtherefore could be suitably used as a rubber composition for tires.

The rubber composition obtained in Example 19 exhibited a low Mooneyviscosity as compared to that of Comparative Example 13 and thereforewas improved in processability. Furthermore, the rubber compositionobtained in Example 19 had a tensile strength at break and a wearresistance which were almost similar to those of Comparative Example 12,but was excellent in rolling resistance performance as compared to thatof Comparative Example 12, and therefore could be suitably used as arubber composition for tires.

From the comparison between Example 19 and Comparative Example 12, itwas confirmed that when the silica (D) was compounded in an amount offrom 0.1 to 150 parts by mass on the basis of 100 parts by mass of therubber component (B), the effects of the present invention could be wellexhibited.

From the comparison between Example 19 and Comparative Example 12, itwas confirmed that when the carbon black (C) was compounded in an amountof from 0.1 to 150 parts by mass on the basis of 100 parts by mass ofthe rubber component (B), the effects of the present invention could bewell exhibited.

From the comparison between Example 19 and Comparative Example 12, itwas confirmed that when the average particle sizes of the carbon black(C) and the silica (D) were controlled to the range of from 5 to 100 nmand from 0.5 to 200 nm, respectively, the resulting rubber compositionexhibited a good processability, was prevented from being deterioratedin mechanical strength, and was excellent in rolling resistanceperformance and wear resistance.

From the comparison between Example 19 and Comparative Example 12, itwas confirmed that even when using two or more kinds of rubbersincluding the natural rubber and the synthetic rubber, the effects ofthe present invention could be well exhibited.

From the comparison between Examples 16 to 18 and Comparative Example 10or 11, it was confirmed that even when using the copolymer (A) incombination with the other components, the effects of the presentinvention could be well exhibited.

TABLE 6 Comparative Example 20 Example 14 Composition (part(s) by mass)Component (A) Copolymer (A-2) 50 Homopolymer of β-farnesene Polyisoprene50 TDAE Component (B) Natural rubber 100 100 Styrene-butadiene rubberButadiene rubber Component (C) Carbon black (C-2) 10 10 Carbon black(C-3) Component (D) Silica (D-1) 90 90 Silica (D-3) Silane couplingreagent 7.2 7.2 Optional Components Stearic acid 2 2 Zinc oxide 3.5 3.5Antioxidant (1) 1 1 Antioxidant (2) 1 1 Sulfur 1.5 1.5 Vulcanizationaccelerator (1) 1.2 1.2 Properties Mooney viscosity (relative value) 94100 Tensile strength at break (relative value) 115 100 Rollingresistance performance 83 100 (at 60° C.; tanδ) (relative value)

From the comparison between Example 20 and Comparative Example 14, itwas confirmed that when the copolymer (A) was compounded in an amount offrom 0.1 to 100 parts by mass on the basis of 100 parts by mass of therubber component (B), the resulting rubber composition exhibited a goodprocessability, and was excellent in rolling resistance performancewithout deterioration in mechanical strength and wear resistance.

From the comparison between Example 20 and Comparative Example 14, itwas confirmed that when the silica (D) was compounded in an amount offrom 0.1 to 150 parts by mass on the basis of 100 parts by mass of therubber component (B), the effects of the present invention could be wellexhibited.

The invention claimed is:
 1. A rubber composition, comprising: (A) acopolymer comprising a monomer unit (a) derived from isoprene and amonomer unit (b) derived from farnesene; (B) a natural rubber as a solerubber component; and (C) carbon black, wherein: contents of thecopolymer (A) and the carbon black (C) in the rubber composition arefrom 0.1 to 100 parts by mass and from 30 to 150 parts by mass,respectively, on the basis of 100 parts by mass of the rubber component(B); and the natural rubber is the only rubber component contained inthe rubber composition.
 2. The rubber composition according to claim 1,wherein the carbon black (C) has an average particle size of from 5 to100 nm.
 3. The rubber composition according to claim 1, wherein acontent of the carbon black (C) in the rubber composition ranges from14.5 mass % to 35.5 mass %, relative to a total mass of the rubbercomposition.
 4. A tire, comprising the rubber composition of claim 1.